When drilling a hole having a comparatively large diameter in a plate-shaped material, a core cutter is conventionally used in light of high drilling efficiency thereof and fineness of an edge of a hole drilled thereby.
In the case of the core cutter having high drilling efficiency, a technical problem is how to smoothly discharge chips. Moreover, a method for solving this problem varies depending on a target object to be drilled, i.e., depending on whether a hole is drilled in wood, concrete, or metal.
For example, when drilling a hole in wood, slits each extending for a predetermined length from a tip end (lower end) of the core cutter to a base end thereof in an axial direction (hole drilling direction) of the core cutter are formed on a peripheral wall of a body portion of the core cutter. With this, the chips are smoothly discharged through the slits to outside. Moreover, when drilling a hole in concrete, the chips are comparatively fine powder. Therefore, cutting blades of the core cutter are formed to project outwardly or inwardly from an outer peripheral surface or inner peripheral surface of the body portion of the core cutter. With this, an adequate gap is formed between the core cutter and an inner peripheral surface of the hole. Thus, the chips are smoothly discharged to outside. Further, when drilling a hole in metal, a tip end portion (lower end portion) of the body portion of the core cutter at which the cutting blades are formed is formed to be thick, and the cutting blades are formed at a rotational-direction front end of this thick portion and are formed at a rotational-direction front portion (in other words, between the thick portions in a rotational direction) concavely toward an inner peripheral side. With this, a discharging groove is formed. Thus, the chips are smoothly discharged through the discharging groove to the base end side. Examples of such prior art are Patent Documents 1 and 2.    Patent Document 1: Japanese Laid-Open Patent Application Publication Hei 4-141309    Patent Document 2: Japanese Laid-Open Patent Application Publication 2003-231013